Structure and method for index-guided buried heterostructure AlGaInN laser diodes

ABSTRACT

An index-guided buried heterostructure AlGalnN laser diode provides improved mode stability and low threshold current when compared to conventional ridge waveguide structures. A short period superlattice is used to allow adequate cladding layer thickness for confinement without cracking. The intensity of the light lost due to leakage is reduced by about 2 orders of magnitude with an accompanying improvement in the far-field radiation pattern when compared to conventional structures.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application(s) No(s). 09/408,458,filed Sep. 29, 1999 now U.S. Pat. No. 6,570,898.

This application is related to commonly assigned, concurrently filedBour et al. U.S. patent application entitled “STRUCTURE AND METHOD FORSELF-ALIGNED, INDEX-GUIDED BURIED HETEROSTRUCTURE AlGalnN LASER DIODES”(application Ser. No. 09/408,415) which is included by reference in itsentirety.

FIELD OF INVENTION

This invention relates to nitride based blue laser diodes.

BACKGROUND OF INVENTION

Nitride based blue laser diodes are being developed for printing andoptical data storage applications. The first AlGalnN laser diodes werebroad area lasers providing no control over the laser diode's variousspatial modes. Most applications, however, require the laser diode tooperate in a single spatial mode. One way of achieving single spatialmode operation for AlGalN blue laser diodes is to use a ridge waveguidestructure to define a lateral waveguide as described in “Ridge-geometrylnGaN multi-quantum-well-structure laser diodes” by S. Nakamura et al.,in Applied Physics Letters 69 (10), pp. 1477-1479 which is herebyincorporated by reference in its entirety. While a ridge waveguideprovides for single spatial mode emission in blue lasers, thewaveguiding provided is relatively weak. The lateral refractive indexstep is small and is influenced by heating and carrier injection.Additionally, there are fabrication difficulties because the ridge mustbe etched to extend sufficiently close to the laser active regionwithout the ability to use an etch stop to prevent material damage tothe laser active region since chemical etching is not applicable to GaNmaterials.

To provide stronger mode stability and low threshold current operation,more strongly index-guided diode lasers are required such as thosehaving buried heterostructures that are typically used for InGaAsP fiberoptic-communication lasers, or the impurity-induced-layer-disorderedwaveguide structures used for high-power single-mode AlGaAs laserdiodes. Additionally, the use of a buried heterostructure avoids certainfabrication difficulties.

BRIEF SUMMARY OF INVENTION

Both index-guided buried heterostructure AlGalnN laser diodes andself-aligned index guided buried heterostructure AlGalnN laser diodesprovide improved mode stability and low threshold current when comparedto conventional ridge waveguide structures. A structure for theindex-guided buried heterostructure AlGalnN laser diode in accordancewith the invention typically uses insulating AlN, AlGaN or p-dopedAlGaN:Mg for lateral confinement and has a narrow (typically about 1-5μm in width) ridge which is the location of the narrow active stripe ofthe laser diode which is defined atop the ridge. The narrow ridge issurrounded by an epitaxially deposited film having a window on top ofthe ridge for the p-electrode contact. The ridge is etched completelythrough the active region of the laser diode structure to the shortperiod superlattice n-cladding layer. Typically, use of a short periodsuperlattice allows doubling of the cladding layer thickness withoutcracking. This reduces the intensity of the light lost due to leakage byabout 2 orders of magnitude with an accompanying improvement in thefar-field radiation pattern in comparison with conventional structures.Junction surfaces are exposed by the ridge etch and these junctionsurfaces contribute surface states which prevent injected carriers fromfilling conduction or valence band states needed for a populationinversion. However, the epitaxial regrowth of a high bandgap materialpassivates the surface states because the interface between theovergrown material and the ridge structure is perfectly coherent.

The structure for the self-aligned, index guided, buried heterostructureAlGalnN laser diode uses the p-cladding layer to also function as theburying layer to provide strong lateral optical confinement and stronglateral carrier confinement. The p-cladding layer/burying layer istypically AlGaN:Mg. The structure for the self-aligned, index guided,buried heterostructure laser diode is simpler than for the index-guided,buried heterostructure AlGalnN laser diode. The laser structure is grownthrough the active quantum well and waveguide region followed by etchinga narrow laser ridge down to the n-bulk cladding layer. The p-typecladding/burying layer is then overgrown around the ridge along with thep-contact layer. Subsequent laser processing is simple since thetwo-step growth process results in a lateral waveguide and carrierconfinement structure which does not require the creation of contactwindows. Hence, the laser processing required is basically a broad arealaser fabrication sequence. Additionally, the comparatively largep-contact area allowed by the self-aligned architecture contributes to alower diode voltage and less heat during continuous wave operation ofthe laser diode.

The advantages and objects of the present invention will become apparentto those skilled in the art from the following detailed description ofthe invention, its preferred embodiments, the accompanying drawingswhich are illustrative and not to scale, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of an index guided, buried heterostructurelaser diode structure in accordance with the invention.

FIG. 2 shows an embodiment of an index guided, buried heterostructurelaser diode structure in accordance with the invention.

FIG. 3 shows an embodiment of a self-aligned, index guided, buriedheterostructure laser diode in accordance with the invention.

FIG. 4 shows the carrier paths for the embodiment shown in FIG. 3.

FIG. 5 shows an embodiment of a self-aligned, index guided, buriedheterostructure laser diode in accordance with the invention.

FIGS. 6-11 show process steps for making a self-aligned, index guided,buried heterostructure laser diode in accordance with the invention.

DETAILED DESCRIPTION

FIG. 1 shows index-guided, buried heterostructure AlGalnN laser diodestructure 100 in accordance with the present invention. GaN:Si layer 115is positioned on Al₂O₃ growth substrate 110 and in one embodiment layer115 may be made of AlGaN:Si to reduce optical leakage. Short periodsuperlattice n-cladding structure 121, typically made up of alternatinglayers of Al_(0.15)Ga_(0.85)N:Si and GaN:Si each with a typicalthickness of about 20 Å, is positioned below the GaN n-waveguide layer(not shown in FIG. 1) at the bottom of InGaN multiple quantum wellstructure 145. Introduction of short period superlattice n-claddingstructure 121 allows increased cladding thickness to significantlyreduce leakage of the transverse optical mode and results in an improvedtransverse far-field pattern for laser diode structure 100. For example,a typical leakage of about 7% may be reduced to 0.5%. The far-field beampattern approaches a Gaussian far-field beam.

P-cladding layer 125, typically Al_(0.07)Ga_(0.93)N:Mg, is positionedover the GaN p-waveguide layer (not shown in FIG. 1) which is adjacentto the tunnel barrier layer (not shown in FIG. 1), typicallyAl_(0.2)Ga_(0.8)N:Mg, present at the top of InGaN multiple quantum wellstructure 145. Layer 185 serves as a capping layer to facilitate ohmiccontact. Burying layer 155 is positioned over capping layer 185,typically GaN:Mg, with windows through burying layer 155 to allowp-electrode 190 to contact GaN:Mg layer 185 and n-electrode 195 tocontact GaN:Si layer 115.

Burying layer 155, typically insulating AlN or AlGaN, has a lowrefractive index which results in strong lateral index guiding becausethe refractive index step is typically around 0.1. With such a largelateral index step, the lateral waveguiding in index-guided, buriedheterostructure AlGalnN laser diode structure 100 overwhelms thermal orcarrier injection influences to provide a more stable and lessastigmatic beam pattern. Burying layer 155 also has a high bandgapenergy which results in high lateral carrier confinement.

Undoped AlN films are insulating and prevent formation of a shunt patharound InGaN multiple quantum well structure 145. In one embodiment ofindex-guided, buried heterostructure AlGalnN laser diode structure 100in accordance with the invention, buried layer 155 is an AlGaN:Mg dopedlayer as undoped AlGaN may not be insulating depending on growthconditions and the aluminum content. The optoelectronic character ofAlGaN depends on growth conditions. For example, it is possible to growinsulating GaN at low temperatures (approximately 900° C.), while athigher growth temperatures GaN tends to have an n-type backgroundconductivity. The precise mechanism for the n-conductivity is presumedto arise from either native defects and or impurities. Oxygen andsilicon are both commonly encountered shallow, unintentional donors inGaN. Low aluminum-content AlGaN that is magnesium doped behavessimilarly to GaN except that the magnesium acceptor's activation energyincreases at the rate of about 3 meV for each percent aluminum added inthe alloy up to a 20 percent aluminum content. For aluminum contentabove 20 percent, unintentional oxygen incorporation may result inuncontrollably high n-type background conductivity. Oxygen is readilyincorporated into AlGaN because of the high affinity of aluminum foroxygen and oxygen impurities are typically available from varioussources during MOCVD growth. While oxygen impurities may be compensatedby magnesium acceptors this is difficult in practice and suggests itwould be difficult to make high aluminum content AlGaN burying layersthat are insulating. High aluminum content provides better optical andcarrier confinement.

Due to the nature of MOCVD growth where atomic hydrogen is available toform neutral complexes with magnesium acceptors, AlGaN:Mg films areinsulating as grown and require thermal annealing to activate p-typeconductivity. While an insulating burying layer is typically preferable,activated AlGaN:Mg (having p-type conductivity) is also suitable forburying layers if it is difficult or not possible to deposit aninsulating burying layer. When buried layer 155 is p-type, a p-njunction is formed at the interface with short period superlatticen-type cladding layer 121. However, the turn-on voltage of this p-njunction is greater than the p-n junction in InGaN multiple quantum wellstructure 145. This favors the current path preferentially going throughInGaN multiple quantum well structure 145. Because no p-GaN cap isdeposited over buried layer 155, the contact of p-electrode 190 toburied layer 155 is significantly more resistive than the contact ofp-electrode 190 to p-GaN:Mg 185. This further favors current injectioninto multiple quantum well structure 145.

An n-type burying layer may also be used in order to further reduceoptical losses because free-carrier loss is lower for n-type material orif it is only possible to grow n-type AlGaN material. FIG. 2 showsindex-guided, buried heterostructure AlGalnN laser diode structure 200with n-burying layer 255 in accordance with an embodiment of theinvention. After regrowth of n-burying layer 255, regrown burying layeris patterned by etching, typically CAIBE. In a second regrowth,n-burying layer 255 is buried with heavily p-doped GaN:Mg layer 250,having a typical doping level of approximately 10²⁰ Mg atoms/cm³, whichalso functions as the contact layer. Alternatively, burying layer 255may also be undoped. P-doped GaN:Mg layer 250 is needed to preventp-electrode 290 from contacting n-burying layer 255.

FIG. 3 shows self-aligned index-guided, buried heterostructure AlGalnNlaser diode structure 300 in accordance with the invention. GaN:Si layer315 is positioned on Al₂O₃ growth substrate 310 and in one embodimentlayer 315 may be made of AlGaN:Si. Bulk n-cladding layer 320, typicallyAl_(0.07)Ga_(0.93)N:Si, is positioned below the GaN n-waveguide layer(not shown in FIG. 3) at the bottom of InGaN multiple quantum wellstructure 345 and over n-cladding short period superlattice 321.N-cladding short period superlattice 321 is typically made up ofalternating layers of AlGaN:Si and GaN:Si each with a typical thicknessof about 20 Å. Bulk n-cladding 320 prevents injection of carriers fromovergrown layer 325, typically Al_(0.07)Ga_(0.93)N:Mg to provideoptimized transverse waveguiding, into the low bandgap portion ofn-cladding short period superlattice 321. Overgrown layer 325 functionsboth as the burying layer and as the upper p-cladding layer. Hence, theoverall thickness of AlGaN in overgrown layer 325 positioned above GaNp-waveguide layer (not shown in FIG. 3) and the tunnel barrier layer,typically Al_(0.2)Ga_(0.8)N:Mg, (not shown in FIG. 3) that are locatedat the top of InGaN multiple quantum well structure 345 is on the orderof the thickness used in conventional nitride lasers. Layer 385,typically GaN:Mg, serves as a capping layer to facilitate ohmic contactto p-electrode 390. Dashed line 303 shows the location of the p-njunction in laser diode structure 300.

Overgrown layer 325 functions as both the p-cladding layer and theburying layer to create both strong lateral current confinement andoptical confinement. The strong lateral index guiding (typically anindex step on the order of 0.1) provided by overgrown layer 325 allowslow threshold current and beam stability. Strong index-guiding allowsthe laser stripe to be made very narrow which facilitates lateral heatdissipation and lowers the required threshold current. The lateral widthof InGaN multiple quantum well structure 345 can be made very narrowbecause of the strong index guiding, typically less than 2 μm, toprovide for a low threshold current and for lateral mode discrimination.Self-aligned index-guided, buried heterostructure AlGalnN laser diodestructure 300 shown in FIG. 3 provides a greater p-contact area thanindex-guided, buried heterostructure AlGalnN laser diode structure 100shown in FIG. 1. A greater p-contact area results in less contactresistance. Lowering contact resistance reduces laser diode heatingparticularly in continuous wave operation and a wider p-contact alsoserves to better dissipate heat. Current preferentially flows throughInGaN multiple quantum well structure 345 because the p-n junctionbandgap is lowest along that portion of dashed line 303.

FIG. 4 is an expanded view of InGaN multiple quantum well structure 345in FIG. 3 and shows carrier injection paths 401 and 402 for self-alignedindex-guided, buried heterostructure AlGalnN laser diode structure 300.P-doped waveguide 407, typically GaN, and n-doped waveguide 408,typically GaN, are also shown. Dashed line 303 traces the location ofthe p-n junction. In an embodiment in accordance with the inventionoperating at a wavelength of about 400 nm, InGaN multiple quantum wellstructure 345 has a bandgap energy of about 3.1 eV while underlyingn-waveguide 408 has a bandgap energy of about 3.4 eV. Hence, the turn-onvoltage for the p-n junction associated with InGaN multiple quantum wellregion 414 is lower than that of the p-n junction associated withn-waveguide 408 and carriers are preferentially injected along injectionpath 401 into InGaN multiple quantum well region 414 when laser diode300 is forward-biased.

The 300 meV difference between the bandgap energy of InGaN multiplequantum well region 414 and n-waveguide 408 may in some cases beinsufficient for confining carrier injection to injection path 401 andsome carriers may be injected along injection path 402 across the p-njunction at the sidewalls of n-waveguide 408. Because carriers injectedacross the p-n junction at the sidewalls of n-waveguide 408 do notpopulate the quantum wells, these carriers do not contribute to higheroptical gain and cause a higher threshold current to be required.Operation at wavelengths higher than about 400 nm such as about 430 nmwould increase the bandgap energy differential so that carrier injectionacross the p-n junction at the sidewalls of n-waveguide 408 issignificantly reduced.

Lateral injection of carriers across the p-n junction at the sidewallsof GaN n-waveguide 408 may be reduced by using an inverted asymmetricwaveguide structure as shown in FIG. 5 which eliminates n-waveguide 408.This eliminates carrier injection along injection path 402 shown in FIG.4. Tunnel barrier layer 546 lies over InGaN multiple quantum well region514 and is typically AlGaN with an aluminum content between 5 to 15percent. P-waveguide 507, typically GaN, is located over tunnel barrierlayer 546. P-cladding layer 525, typically AlGaN:Mg, covers p-waveguide507 and buries entire laser ridge structure 511. Capping layer 585,typically GaN:Mg, provides contact to p-contact 590.

InGaN multiple quantum well region 514 is positioned on bulk n-claddinglayer 520, typically AlGaN:Si. Bulk n-cladding layer 520 is placed overshort period superlattice n-cladding structure 521, typically made up ofalternating layers of AlGaN:Si and GaN:Si with each with a typicalthickness of about 20 Å. Bulk n-cladding layer 520 blocks chargecarriers from being injected from p-cladding layer 525 into thetypically lower bandgap GaN:Si layers of short period superlatticen-cladding structure 521. Introduction of short period superlatticecladding structure 521 allows cladding layers with the same averagealuminum content as bulk n-cladding layer 520, typically about 8percent, to be grown to a thickness of more than 1 micron whereas bulkn-cladding layer 520 is usually limited to a typical thickness of about0.5 μm before cracking occurs. Increased thickness provided by shortperiod superlattice cladding structure 521 significantly reduces leakageof the transverse optical mode and results in an improved transversefar-field pattern for laser diode structure 500. For example, a typicalleakage of about 7% may be reduced to 0.5%. The far-field beam patternapproaches a Gaussian far-field beam. N-layer 515, typically AlGaN:Si orGaN:Si, underlies short period superlattice cladding structure 521 andis placed over substrate 510, typically Al₂O₃.

Index-guided, buried heterostructure AlGalnN laser diode structure 100in FIG. 1 may be fabricated by first CAIBE (chemically assisted ion beametch) etching through layers 185, 125, 145 and 121 to expose n-typelayer 115 for deposition of n-electrode 195. Growth related to GaN isdisclosed in U.S. patent application Ser. No. 09/288,879 entitled“STRUCTURE AND METHOD FOR ASYMMETRIC WAVEGUIDE NITRIDE LASER DIODE” byVan de Walle et al. hereby incorporated by reference in its entirety. Apossible issue with p-type material growth is magnesium turn on delaydue to Cp₂Mg sticking to gas lines rather than entering the reactor.Magnesium turn on delay may be compensated for by pre-flowing Cp₂Mg intothe reactor prior to heating and growth. The magnesium is switched tovent during the heatup and then switched back into the reactor withoutturn on delay when magnesium doping is desired.

In one embodiment in accordance with the present invention, photoresistis applied to GaN:Mg layer 185 to define the top of ridge structure 111.However, before applying the photoresist it is advantageous to activateGaN:Mg layer 185. The activation avoids possible hydrogen evolutionduring processing which causes bubbling under the photoresist.Activation is typically performed in one of two ways. Normal thermalactivation may be used by heating to approximately 850° C. for 5 minutesin a nitrogen environment. Alternatively, GaN:Mg layer 185 may beexposed to intense UV light to release the hydrogen preventing possiblethermal degradation of the surface. The photoresist stripe islithographically patterned with the photoresist stripe aligned along the<1100> crystallographic direction of GaN layer 185. Subsequently, thestripe is etched to produce a ridge structure 111, typically having awidth from 1 to 5 μm.

Ridge structure 111 is formed by CAIBE etching through layers 185, 125,145 to short period superlattice n-cladding structure 121. Note that thelength axis of ridge structure 111 is oriented perpendicular to the setof {1100} planes and aligned along the <1100> crystallographic directiondue to the orientation of the photoresist stripe prior to etching. Thisorientation has been found to reduce surface pitting.

Cleaning is performed prior to epitaxial regrowth and includesphotoresist removal using a combination of dissolution in acetone andashing in an oxygen plasma. Further cleaning is performed using aquaregia then H₂SO₄:H₂O₂:H₂O mixed in the ratio 4:1:1, respectively andused as-mixed (hot). A final rinse is performed with de-ionized waterfollowed by drying in pure nitrogen.

The regrowth occurs at a stabilized temperature of 900° C. in anammonia/hydrogen gas stream. When the growth temperature has stabilizedthe reactants trimethylaluminum, trimethylgallium andbiscyclopentadienylmagnesium are introduced into the reactor. Insulatingovergrowth of burying layer 155 is accomplished by growing an undopedfilm at low temperature (T_(growth)<900° C.). Epitaxial regrowth ofburying layer 155, typically made of insulating AlN or AlGaN, isperformed to surround the ridge structure. Alternatively, a p-dopedburying layer 155, typically AlGaN:Mg may be grown. An opening is etchedusing CAIBE into burying layer 155 down to p-cap 185 to open up a narrowwindow for contacting p-cap layer 185 with p-electrode 190.

Further processing of index-guided, buried heterostructure AlGalnN laserdiode structure 100 involves p-dopant activation by annealing at 850° C.for 5 minutes in a nitrogen ambient. Palladium p-contact metaldeposition is evaporatively deposited and alloyed at 535° C. for 5minutes. Mirror facets (not shown) are formed by cleaving or etching. Ifmirror facets are etched, the etch of the first mirror facet isperformed along with the mesa etch. N-metal deposition is performed ofTi/Al. Finally, n-electrode 195 and p-electrode 190 are deposited andhigh reflection coatings TiO₂/SiO₂ are applied to the first and secondmirrors.

Processing for laser structure 200 is similar to that of laser structure100. However, in FIG. 2 n-type burying layer 255, typically AlGaN:Si, isregrown followed by regrowth of p-burying layer 250, typically GaN:Mg.Additionally, after n-metal deposition takes place, high temperaturedielectric deposition, typically of SiN or SiO₂, is performed over theentire surface using PECVD (plasma enhanced chemical vapor deposition).The deposited dielectric is then patterned to create windows forn-electrode 195 and p-electrode 190. Patterning is used instead of aphotoresist mask because the deposition temperature for the dielectricis approximately 250° C. and photoresist is limited to temperaturesbelow about 120° C. This makes a restricted contact window forp-electrode 290 contacting p-burying layer 250 to avoid currentinjection outside the laser stripe. Alternatively, ion implantation atenergies typically from about 80-120 keV may be used to create therestricted window by masking the window regions and then performing theion implantation.

Processing for self-aligned, index guided, buried heterostructureAlGalnN laser diode structures 300 (see FIG. 3) and 500 (see FIG. 5) issimilar to that for laser diode structures 100 and 200. A key differenceof the self-aligned, index guided, buried heterostructure AlGalnN laserstructures 300 and 500 is that the deposited p-doped layers 325 and 525serve both as p-cladding layers and as burying layers. Due to theself-aligned structure of laser diodes 300 and 500 there is also noetching through burying layers 325 and 525, respectively. Note thatprocessing is performed so that the length axis of both ridge structure311 (see FIG. 3) and ridge structure 511 (see FIG. 5) is aligned alongthe <1100> crystallographic direction to reduce surface pitting.

FIGS. 6-11 show processing steps for making a laser diode structuresimilar to self-aligned, index guided, buried heterostructure AlGalnNlaser diode structure 300. Tunnel barrier layer 646, if desired, liesbetween multiple quantum well region 345 and p-doped waveguide 407.

FIG. 6 shows the deposited epitaxial structure up to and through p-dopedwaveguide region 407. Note that no p-cladding or capping layers arepresent. FIG. 7 shows the CAIBE etching of trenches 710, typically about10 μm wide, surrounding ridge 720 which is typically about 1-2 μm wide.The etching must penetrate into, but not through bulk n-cladding layer320. This results in an etch of about 300 nm for a typical thickness ofmultiple quantum well region 345 and waveguides 407 and 408. FIG. 8shows MOCVD growth of p cladding layer 325 to a typical thickness ofabout 0.5-1.0 μm. P-capping layer 385 is also grown to a typicalthickness of about 0.1 μm over the structured surface. The remainingprocess sequence is similar to that of conventional ridge-waveguidenitride lasers except that the ridge-etch step is not performed.

FIG. 9 shows deposition of p-metal layer 390, typically palladium alloy,at 535° C. for 5 minutes in a nitrogen ambient. FIG. 10 shows CAIBEetching of p-metal layer 390 and CAIBE etching to a depth of about 2 μmto penetrate through n-cladding short period superlattice 321 intoGaN:Si layer 315. This etch exposes the area for n-lateral contact 1101.The first and second mirrors (not shown) are also CAIBE etched in thisstep. Liftoff metallization (typically Ti—Al) is performed for n-contactpad 395. FIG. 10 shows metallization, typically Ti—Au, to build up metalthickness on n-contact 1101 and p-contact 1102. Finally, SiO₂/TiO₂mirror coating evaporation is performed.

While the invention has been described in conjunction with specificembodiments, it is evident to those skilled in the art that manyalternatives, modifications, and variations will be apparent in light ofthe foregoing description. Accordingly, the invention is intended toembrace all such alternatives, modifications, and variations that fallwithin the spirit and scope of the appended claims.

1. A method for making a nitride light emitting structure comprising theoperations of: providing a ridge structure having an active region;adding a burying layer including nitride, the material in the buryinglayer doped throughout in one of a group of n-doped, p-doped or undoped,the burying layer overlying said ridge structure, said ridge structureforming a guiding surface where the burying layer contacts the activeregion, the guiding surface providing index guiding in the ridgestructure during operation of the light emitting structure.
 2. Themethod of claim 1 wherein the ridge structure includes a lower claddinglayer below the active region, said lower cladding layer being ashortperiod superlattice.
 3. The method of claim 1 wherein said ridgestructure is oriented along the <1100> crystallographic direction. 4.The method of claim 1 wherein said burying layer is p-doped throughout.5. The method of claim 1 wherein a tunnel barrier layer adjoins amultiple quantum well structure in the ridge structure.
 6. A method formaking a nitride light emitting structure comprising the operations of:providing a ridge structure having a multiple quantum well structure;adding a first burying layer including nitride overlying said ridgestructure, the first burying layer doped throughout with a singlecarrier type of one of a group of either n type, p type or intrinsic,said first burying layer having an opening to said third surface of saidridge structure for electrical contact, a guiding surface forming wherethe first burying layer contacts the multiple quantum well structure,the guiding surface providing index guiding in the ridge structureduring operation of the light emitting structure; and adding a secondburying layer overlying said first burying layer, such that said secondburying layer is in contact with said a top surface of said ridgestructure.
 7. The method of claim 6 wherein said first burying layer isn-doped.
 8. The method of claim 6 wherein said second burying layer iscomprised of magnesium doped GaN.
 9. The method of claim 6 wherein saidridge structure is oriented along the <1100> crystallographic direction.10. The method of claim 6 wherein said cladding structure is ashortperiod superlattice.
 11. The method of claim 6 wherein theoperation of providing a ridge structure is an etching process.
 12. Themethod of claim 11 wherein the etching is a reactive ion etch.
 13. Themethod of claim 11 wherein the etching is an ion beam etching.
 14. Themethod of claim 6 wherein the operation of adding a first burying layeris by growing the first burying layer.
 15. The method of claim 12wherein a metal organic chemical vapor deposition is used in the growingprocess.
 16. The method of claim 13 wherein the opening in the buryinglayer is formed by etching the burying layer.
 17. The method of claim 1wherein the providing of the ridge structure uses an etching process.18. The method of claim 17 wherein the etching process is a reactive ionetch.
 19. The method of claim 17 wherein the etching process is an ionbeam etch.
 20. The method of claim 17 wherein the etching process is achemical assisted ion beam etching process.
 21. The method of claim 17wherein the etching process is en inductively coupled plasma etch. 22.The method of claim 1 wherein the operation of adding a burying layerinvolves growing the burying layer.
 23. The method of claim 1 whereinmetal organic chemical vapor deposition is used to grow the buryinglayer.
 24. The method of claim 1 further comprising the operation of:etching an opening into the burying layer, the opening to provide anelectrical contact.
 25. The method of claim 6 wherein the first buryinglayer is p-doped.
 26. A method for making a nitride light emittingstructure comprising the operations of: providing a ridge structurehaving an active region; adding a burying layer including nitride, theburying layer n-doped throughout, the burying layer overlying said ridgestructure, said ridge structure forming a guiding surface where theburying layer contacts the active region, the guiding surface providingindex guiding in the ridge structure during operation of the lightemitting structure.
 27. A method for making a nitride light emittingstructure comprising the operations of: providing a ridge structurehaving an active region; epitaxially depositing a burying layerincluding nitride, the burying layer undoped throughout, the buryinglayer overlying said ridge structure, said ridge structure forming aguiding surface where the burying layer contacts the active region, theguiding surface providing index guiding in the ridge structure duringoperation of the light emitting structure.